A highly robust self-supporting three-dimensional porous anode and its preparation method and application

Abstract

The present invention relates to a highly robust self-supporting three-dimensional porous anode and a preparation method and application thereof. It is prepared by a pressing forming and heat treatment process with electrocatalytically active substances as the basis and engineering fibers as the pore-forming agent. A highly robust self-supporting three-dimensional porous anode is obtained by a simple process, which can electrocatalytically oxidize and remove organic pollutants efficiently, rapidly and stably, and is conducive to large-scale industrial production and application.

Description

Technical Field

[0001] The present invention relates to an anode and its preparation method and application, belonging to the field of electrocatalytic oxidation. Background Art

[0002] In the process of electrocatalytic oxidation for removing persistent organic pollutants, the performance of the anode catalytic electrode determines the oxidation and removal effect of pollutants. Currently, there are two preparation methods for anodic catalytic electrodes based on electrocatalytic active substance powders: a planar-structured anode with a flat substrate coated with powder catalysts and a self-supporting three-dimensional structured anode obtained by pressing and sintering powder tablets. Compared with the planar-structured anode, the self-supporting three-dimensional anode has the advantages of simple composition, uniform structure, rich porosity, etc., which is more conducive to the rapid and stable progress of the electrochemical oxidation reaction. During the preparation process of the self-supporting three-dimensional anode, a pore-forming agent can be used to form pores inside and on its surface, increasing the specific surface area and the number of exposed active sites of the self-supporting three-dimensional anode, thereby accelerating the migration and oxidative degradation of pollutants in the pores. The pyrolysis temperature not only affects the presence of the pore-forming agent and the binder in the final material but also affects the sintering effect between electrocatalytic active substance particles. Therefore, the selection of the pore-forming agent and the pyrolysis temperature has an important influence on the structure and performance of the finally formed self-supporting three-dimensional anode.

[0003] Currently, commonly used pore-forming agents include ammonium carbonate, ammonium bicarbonate, carbon fiber, starch, etc. However, ammonium carbonate and ammonium bicarbonate have complex compositions; carbon fiber has a high decomposition temperature and is difficult to be completely removed during low-temperature pyrolysis; such pore-forming agents are prone to residual elements forming impurities that affect the electrode performance. And starch is prone to swelling, resulting in poor pressing and molding effects, and the electrode sheets obtained by pyrolysis are incomplete or even broken, which is not conducive to large-scale popularization and application.

[0004] Engineering fiber is a micron-scale synthetic fiber mainly composed of polypropylene, commonly used in construction engineering, with low cost, wide source, and easy availability. And it only contains carbon and hydrogen elements, has a low thermal decomposition temperature, and does not react with water, and there has been no application report in the field of fine synthesis. Summary of the Invention

[0005] The purpose of the present invention is to provide a highly robust self-supporting three-dimensional porous anode with high mechanical strength and degradation performance, as well as its preparation method and application. By selecting low-cost and easily available engineering fiber as a new pore-forming agent and through a simple synthesis process, a porous anode with high mechanical strength and high robustness is obtained, solving the problems of low mechanical strength, low degradation efficiency, and poor stability of the existing three-dimensional porous anode, and being more conducive to wide application in actual production.

[0006] According to the first aspect of the present invention, the present invention provides a highly robust self-supporting three-dimensional porous anode, which is characterized by including the following steps:

[0007] Step 1: Mix the electrocatalytic active material evenly with the pore former and the binder to obtain a mixed powder;

[0008] Step 2: Extrude the mixed powder obtained in Step 1 into the desired shape to obtain a three-dimensional anode precursor;

[0009] Step 3: Pyrolyze the anode precursor obtained in Step 2 to obtain a highly robust self-supporting three-dimensional porous anode.

[0010] Among them, the pore former in Step 1 is engineering fiber or a combination of engineering fiber and other pore formers.

[0011] Preferably, the electrocatalytic active material is one or a combination of titanium oxide, tin oxide, lead oxide and their C, N, B, F, Ni, Fe, La, Cu, Ce, Nb dopants.

[0012] Preferably, the binder is one or a combination of paraffin, cyclodextrin, chitosan, polyvinylidene fluoride, methylcellulose, sodium alginate.

[0013] Preferably, the mass ratio of the electrocatalytic active material to the pore former in Step 1 is 1:0.01 - 1:0.1.

[0014] Preferably, the pressure required for pressing and forming in Step 2 is 10 - 25 bar, and the action time is 5 - 30 min.

[0015] Preferably, the pyrolysis atmosphere in Step 3 is air, the pyrolysis temperature is 400 - 1800 °C, and the pyrolysis time is 1 - 12 hours.

[0016] According to the second aspect of the present invention, the present invention provides a highly robust self-supporting three-dimensional porous anode, which is characterized in that it has high mechanical strength, typically the hardness and toughness are higher than 150 N, the elasticity is greater than 0.7, and the cohesion is greater than 0.9.

[0017] According to the third aspect of the present invention, the present invention provides an application of a highly robust self-supporting three-dimensional porous anode in electrocatalytic oxidation for degrading pollutants.

[0018] The beneficial effects of the present invention are as follows:

[0019] (1) The pore former has low cost and is easy to obtain. At the same time, the synthesis process is simple, which is conducive to large-scale production. Compared with pore formers such as carbon fiber, fructose, and starch, the dosage of engineering fiber is small, only 1% - 10% of the weight of the electrocatalytic active material is required; and the price of engineering fiber is low, only one-tenth of the price of the carbon fiber pore former of the same weight and one-half of the price of fructose, so it is more conducive to popularization and application.

[0020] (2) By utilizing the characteristics of engineering fibers to replace the existing pore-forming agents, a highly robust self-supporting three-dimensional porous anode with high mechanical strength and degradation performance can be obtained. It does not absorb moisture at normal temperature and pressure, and can form a random support system in the three-dimensional anode precursor, effectively promoting the integrity of the pyrolyzed electrode. In contrast, fructose and starch are prone to moisture absorption, and it is difficult to avoid obtaining broken electrodes when prepared in ordinary air, which is not conducive to popularization and application. Moreover, the pyrolysis temperature of engineering fibers is relatively low (the typical value is not higher than 200 °C), and there will be no residue even during low-temperature pyrolysis (the typical value is 500 - 1000 °C); while carbon fibers with a high pyrolysis temperature (1100 - 1350 °C) have more carbon impurities remaining after the same low-temperature pyrolysis, resulting in an increase in the energy consumption of the anode material obtained by this method in electrocatalytic oxidation applications, which is not conducive to popularization and application. In addition, the N element contained in ammonium carbonate and ammonium bicarbonate not only causes nitrogen-containing gas pollution to the atmosphere during the pyrolysis process, but may also form doping on the shallow surface of electrocatalytic active substance particles, and is easily dissolved and detached during subsequent electrocatalytic oxidation applications. Therefore, the stability of the anode material obtained by this method in electrocatalytic oxidation applications is insufficient, which is not conducive to popularization and application. Description of the Drawings

[0021] Figure 1 Photograph of the physical object of the highly robust self-supporting three-dimensional porous anode prepared in Example 1

[0022] Figure 2 Scanning electron microscope photograph of the highly robust self-supporting three-dimensional porous anode prepared in Example 1

[0023] Figure 3 Pore size distribution diagram of the self-supporting three-dimensional porous anode prepared in Example 1

[0024] Figure 4 Mechanical strength index diagram of the highly robust three-dimensional porous anode prepared in Example 1

[0025] Figure 5 Cyclic stability test results of the highly robust three-dimensional porous anode prepared in Example 1

[0026] Figure 6 Scanning electron microscope photograph of the three-dimensional porous anode prepared in Comparative Example 2 Detailed Embodiments

[0027] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be given in conjunction with the accompanying drawings. The following content is only an example and illustration of the inventive concept. Those skilled in the art can make various modifications or supplements to the described specific embodiments, or use similar methods to replace them, as long as they do not deviate from the inventive concept or exceed the scope defined by the claims of the present invention, they shall fall within the protection scope of the present invention.

[0028] Example 1

[0029] The preparation process of the three-dimensional porous electrocatalytic anode includes the following steps:

[0030] Step 1: Under normal temperature, normal pressure and air conditions, use a vortex mixer to uniformly mix 1.2 g of SnO2-Sb nano powder, 0.01 g of engineering fiber and 0.06 g of chitosan powder to obtain a mixed powder;

[0031] Step 2: Uniformly distribute the mixed powder obtained in Step 1 in a mold, place the mold in a tablet press, apply a vertical pressure of 20 bar for 10 min to obtain a formed three-dimensional anode precursor;

[0032] Step 3: Pyrolyze the anode precursor obtained in Step 2 in air at 1000 °C for 12 hours to remove the engineering fiber and chitosan, and obtain a highly robust self-supporting three-dimensional porous anode. The physical diagram is as Figure 1 shown.

[0033] The scanning electron microscope photograph of the highly robust self-supporting three-dimensional porous anode obtained in this example is as Figure 2 shown, its pore size distribution is as Figure 3 shown, and the mechanical strength index is as Figure 4 shown. The electrocatalytic anode presents a dark blue color, has a complete disc morphology, a diameter of 2.5 cm, and a thickness of about 1 mm. The electrode has relatively rich mesopores and macropores, and the average pore size is about 57 nm. In addition, the electrode also has high hardness, toughness, elasticity and cohesion, and the corresponding data of each index are 172.82, 162.97, 0.82 and 0.95 respectively, which is suitable for large-scale production.

[0034] The application of the three-dimensional porous electrocatalytic anode in degrading pollutants:

[0035] Use the self-supporting three-dimensional porous electrode in this example as the anode, a platinum sheet as the cathode, a silver / silver chloride electrode as the reference electrode, and 0.1 mol L -1 Na2SO4 as the electrolyte to degrade atrazine in a single-chamber electrolytic cell. Figure 5 is the cyclic stability test result of atrazine degradation. It can be seen from the figure that the highly robust self-supporting three-dimensional porous anode can efficiently and rapidly degrade atrazine and has high long-term stability, which is beneficial to practical popularization and application.

[0036] Comparative Example 1

[0037] Compared with Example 1, ammonium bicarbonate was used as the pore-forming agent while other conditions were the same. During the pyrolysis process, the ammonium bicarbonate pore-forming agent generates ammonia gas and escapes, which is likely to cause air pollution. Moreover, the nitrogen element in ammonium bicarbonate is extremely easy to form doping on the shallow surface of the electrocatalytic active material particles during the pyrolysis process, and it is also easy to dissolve and detach during subsequent electrocatalytic oxidation applications. Therefore, the obtained anode material has insufficient stability in electrocatalytic oxidation applications.

[0038] Comparative Example 2

[0039] Compared with Example 1, carbon fiber was used as the pore-forming agent while other conditions were the same. The pyrolysis temperature required for preparing the electrode needs to be higher than 1200 °C to completely remove the carbon fiber. Figure 6 Figure Figure 6 shows the SEM image of the electrode obtained by using carbon fiber as the pore-forming agent at a pyrolysis temperature of 800 °C. Moreover, the mechanical strength of the electrode prepared by this method is relatively low, and its brittleness is so poor that it cannot be measured by a texture analyzer. The hardness, elasticity, and cohesiveness are 140.36, 0.74, and 0.95 respectively, which are far lower than those of the electrocatalytic anode prepared with engineering fiber as the pore-forming agent. In addition, its price is more than ten times that of the same weight of engineering fiber. Therefore, using engineering fiber as the pore-forming agent has advantages in terms of cost and mechanical strength compared to using carbon fiber.

[0040] Comparative Example 3

[0041] Compared with Example 1, starch was used as the pore-forming agent while other conditions were the same. During the mixing process in Step 1, starch is prone to hygroscopic agglomeration when directly prepared in the air, which is not conducive to the uniform dispersion of the pore-forming agent, electrocatalytic active powder material, and binder, nor is it conducive to the stable forming of the electrode precursor. Therefore, using engineering fiber as the pore-forming agent has the advantage of lower requirements for manufacturing conditions compared to using starch.

[0042] Example 2

[0043] The preparation process of the three-dimensional porous electrocatalytic anode includes the following steps:

[0044] Step 1: Mix 1.2 g of PbO2 nano-powder, 0.1 g of engineering fiber, and 0.08 g of paraffin evenly to obtain a mixed powder;

[0045] Step 2: Evenly distribute the mixed powder obtained in Step 1 in a mold, place the mold in a tablet press, apply a vertical pressure of 10 bar for 30 minutes to obtain a formed three-dimensional anode precursor;

[0046] Step 3: Pyrolyze the anode precursor obtained in Step 2 at 800 °C in the air for 12 hours to obtain a highly robust self-supporting three-dimensional porous anode.

[0047] Example 3

[0048] The preparation process of the three-dimensional porous electrocatalytic anode includes the following steps:

[0049] Step 1: Mix 1.2 g of TiO2 powder, 0.08 g of engineering fiber, and 0.08 g of methyl cellulose evenly to obtain a mixed powder.

[0050] Step 2: Evenly distribute the mixed powder obtained in Step 1 in a mold, place the mold in a tablet press, apply a vertical pressure of 25 bar for 5 minutes to obtain a formed three-dimensional anode precursor.

[0051] Step 3: Pyrolyze the anode precursor obtained in Step 2 at a high temperature of 1800 °C in air for 3 hours to obtain a highly robust self-supporting three-dimensional porous anode.

[0052] Example 4

[0053] The preparation process of the three-dimensional porous electrocatalytic anode includes the following steps:

[0054] Step 1: Under normal temperature, pressure, and air conditions, mix 1.2 g of SnO2-F nano powder, 0.12 g of engineering fiber, and 0.03 g of cyclodextrin evenly to obtain a mixed powder.

[0055] Step 2: Evenly distribute the mixed powder obtained in Step 1 in a mold, place the mold in a tablet press, apply a vertical pressure of 25 bar for 5 minutes to obtain a formed three-dimensional anode precursor.

[0056] Step 3: Pyrolyze the anode precursor obtained in Step 2 in air at 400 °C for 6 hours to obtain a highly robust self-supporting three-dimensional porous anode.

[0057] Example 5

[0058] Compared with Example 1, the active material is B, N-doped TiO2 nano powder, and the pyrolysis temperature is 1600 °C. This three-dimensional porous electrocatalytic anode can rapidly degrade 99.95% of levofloxacin in the electrolyte in 60 minutes in a single-chamber electrolytic cell.

[0059] Example 6

[0060] Compared with Example 1, the active material is La-doped TiO2 nano powder, the binder is 0.12 g of cyclodextrin, and the pyrolysis temperature is 1300 °C. This three-dimensional porous electrocatalytic anode can rapidly degrade 99.95% of bisphenol A in the electrolyte in 60 minutes in a single-chamber electrolytic cell.

[0061] The above are only exemplary embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A highly robust self-supporting three-dimensional porous anode, characterized in that: The specific surface area is 12 - 70 m 2 g -1 , the particle size of the electrocatalytic active substance is 20 - 500 nm, the hardness and toughness of the electrode are higher than 150 N, the elasticity is greater than 0.7, and the cohesion is greater than 0.9; The preparation method of the highly robust self-supporting three-dimensional porous anode includes the following steps: Step 1: Under normal temperature, normal pressure and air conditions, uniformly mix an electrocatalytically active substance with a pore-forming agent binder to obtain a mixed powder; Step 2: Press the mixed powder obtained in Step 1 into shape to obtain a self-supporting three-dimensional anode precursor; Step 3: Pyrolyze the anode precursor in Step 2 to obtain a highly robust self-supporting three-dimensional porous anode; The pore-forming agent is engineering fiber or a combination of engineering fiber and other pore-forming agents; The electrocatalytically active substance is titanium oxide, tin oxide, lead oxide, or a combination of one or more of the above oxides doped with N, B, F, Ni, Fe, La, Cu, Ce, Nb; In Step 1, the mass ratio of the electrocatalytically active substance to the pore-forming agent is 1:0.01 to 1:0.

1.

2. The preparation method of the highly robust self-supporting three-dimensional porous anode according to claim 1, characterized in that, The binder is one or a combination of paraffin, cyclodextrin, chitosan, polyvinylidene fluoride, methyl cellulose, sodium alginate.

3. The preparation method of the highly robust self-supporting three-dimensional porous anode according to claim 2, characterized in that, In Step 2, the pressure required for pressing into shape is 10 to 25 bar, and the action time is 5 to 30 min.

4. The preparation method of the highly robust self-supporting three-dimensional porous anode according to claim 3, wherein In Step 3, the pyrolysis atmosphere is air, the pyrolysis temperature is 400 to 1800 °C, and the pyrolysis time is 1 to 12 hours.

5. The application of the highly robust self-supporting three-dimensional porous anode according to claim 4 in electrocatalytic oxidation.

6. The application according to claim 5, characterized in that, The application is to carry out the oxidation and degradation of pollutants.

7. The application according to claim 6, wherein The pollutants are one or a mixture of levofloxacin, sulfadiazine, tetracycline, amoxicillin, bisphenol A, atrazine, rhodamine B, phenol.

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